Interpretive Summary: Protection of grain and cereal products against damage and contamination by insects during storage, processing, and marketing has relied heavily on routine application of chemical insecticides. However, increasing concern about the health and environmental hazards of insecticide application, has made it necessary to seek new pest control methods that employ insecticides sonly as needed. These new methods will require pest monitoring to determin timing and location of control intervention. Effective insect traps have been developed for this purpose, but their usefulness has been limited by our inability to use numbers of insects trapped in estimating numbers of insects actually present, or in making pest management decisions. Scientists at the USDA, ARS, Center for Medical, Agricultural and Veterinary Entomology, Gainesville, FL, established relationships between grain temperature and numbers of insects trapped that will be useful to researchers in developing methods for converting numbers captured at various temperatures to pest management recommendations.

Technical Abstract:
A series of trap samples can be used to estimate relative changes in abundance, provided the proportion of the population trapped remains constant; that is, it is not affected by population density or by changing environmental conditions. However, we know too little about the influence of these factors to evaluate the validity of trap catch as an estimate of relative abundance. In the present study, we used data sets from stored corn to determine seasonal trends in grain temperature and capture rates of two stored-product beetles, Typhaea stercorea (L.) and Tribolium castaneum (Herbst), and to examine the association between grain temperature and trap catch. Mean weekly temperature and weekly trap catch were fitted to cubic polynomials, which expressed changes over time (from all causes) in temperature and trap catch, and were used to eliminate seasonal trends by calculating residuals (observed values - predicted values). Correlation analysis showed a strong association between trap catch and temperature that disappeared, or was greatly weakened, when residuals, rather than raw data were analyzed to eliminate seasonal trends. This, along with other features of the data, suggested that population density was, in general, more important than the effect of temperature on insect activity in determining trap catch. Thus, temperature variation should not pose a serious problem in estimating relative abundance, as long as mean temperature during the trapping period remains above the activity threshold of the insects. More information on the relationship between temperature and species specific activity levels is needed to refine our interpretation of trap catch.